Process of making rustless iron and similar alloys



Dec. 29, 1925. 7,

Percenfaye 60/1600.

F. M. BECKET PROCESS OF MAKING RUSTLESS IRON AND SIMILAR ALLOYS Filed Feb. 21, 1925 7'0 Carbon Confer)? f Fermarame SW/can.

QM 5%. M

Patented Dec. 29, 1925.

PATENT OFFICE.

FREDERICK M. BECKET, OF NEW YORK, N. Y.

PROCESS OF MAKING RUSTLESS IRON AND SIMILAR ALLOYS.

Application filed February 21, 1925. Serial No. 10,852.

To all whom it may concern:

Be it known that I, FREDERICK M. BECKET, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Processes of Making Rustless Iron and Similar Alloys, of which the following is a specification. v

This invention relates to the manufacture of corrosion-resisting chromium alloys of which the alloy known to the trade as rustless iron istypical. As is now well understood in this art, rustless iron is a readily workable alloy usually containing about 8-18% of chromium, although either higher or lower percentagesmay be used. It is necessarily a low-carbon product, the carbon content being below 0.15% and preferably below 0.10%. The balance is principally iron, usually with small percentages of silicon and manganese and at times of other metals, for example nickel.

The necessity of securing an extremely low carbon content in rustless iron is the cause of serious difiiculties in its manufacture. Molten chromium alloysof this type absorb carbon with great avidity, and it is only by the exercise of extraordinary precautions that carbon is excluded from the product to the desired extent.

In Patent No. 1,508,211, granted to me on Sept. 9, 1924, I have described a process for making rustless iron and similar rust-resisting chromium alloys wherein an oxygencontaining compound of chromium, such as chromite, is caused to react with ferrochromesilicon to reduce the chromite or the like and oxidize the silicon, producing an iron-chromium alloy suitablefor the manufacture of rustless iron or other corrosionresisting alloys. The present invention comprises a process utilizing the reaction between a high silicon alloy and chromite or, other metal oxid, and it includes ferro chrome-silicon alloys of novel composition suitable for use in such process.

.My invention is based on my investigation of the relation between the silicon and carbon contents of ferrochrome-siliconi An extensive series of ferrochrome-silicons was prepared under strictly comparable electric furnace conditions with the silicon content varying between 17% and 67%, and the carbon content of eachalloy was determined. The relation between carbon content and silicon content is shown by the curve of the annexeddrawing, wherein the percentages of the two constituents are plotted as ordinates and abscissee respectively. From an inspection of the curve it is apparent that as the silicon content increases the carbon in the alloy diminishes very rapidly until the silicon reaches about 40%. As the silicon increases beyond this point, the carbon content is only slightly diminished, and after the silicon has increased to about 50%, there is little or no further decrease in the carbon content. A considerable quantity of iron will usually be admixed with the reaction product of the ferrochrome-silicon and the chromite or the like for:.the production of the corrosion-resisting chromium alloys contemplated herein, and iron of very low carbon content is of course available; but it is nevertheless highly advantageous to keep the carbon content of the ferrochrome-silicon below about 0.10%. It is desirable to carry out the reaction between the alloy and the chromite in an electric furnace with carbon or graphite electrodes, and if dilution with iron as a separate step, is resorted to, it is of advantage to be able to carry out this dilution in the same or a similar furnace, but the absorption of a certain amount of carbon by a chromium alloy when treated in this type of furnace is inevitable. It is therefore desirable to decrease the carbon content of the ferrochrome-silicon to the lowest possible percenta e, since this tends to avoid the necessity for special measures to mini mize the introduction of carbon from the electrodes or from other adventitious sources. Moreover, with similar precautions to exclude carbon from sources other than the ferrochrome-silicon, it permits a final product of lower carbon content to be made.

I therefore prefer to employ ferrochromesilicon containing upward of about 40% of silicon and correspondingly low in carbon. So far as I am aware such alloys had not been prepared prior to my invention, and I therefore claim them per se in the appended claims. Since increasing the silicon beyond 50% causes'little or no decrease in the'carbon content, my preferred range for silicon is between 40-and 50%, with a cor- E mample I The charge mixture contained in each 1000 lbs.: I

Pounds. Quartzite 420 Chromite 244 Carbonaceous reducing agent 336 The alloy produced analyzed as follows:

Per cent.

- Cr 29. 33 C 0.05

Example I].

The charge mixture contained in each 1000 lbs.:

Pounds.

Quartzite 480 Chromite 160 Carbonaceous reducing agent 360 The alloy produced analyzed as follows:

Percent.

Si 64. 13 Cr 22. 63 C 0. 04

The following examples illustrate the production of rustless iron using the ferrochrome-silicons produced in Examples I and II.

E wa aple I l I p,

The charge mixture contained in each 1000 lbs.:

Pounds. Ferrochrome silicon from Example I 93 Chromite 216 Iron (under 0.10% carbon) 518 Lime 173 The rustless iron analyzed as follows:

' Per cent.

Cr 15. 22 C T 0.12 Si O. 25

with the balance principally iron.

E mample IV.

The charge mixture contained in each 1000 lbs.:

Ferrochrome silicon. from Ex- Pounds. ample II 75 Chromite 236 Iron (under 0.10% carbon) 500 Lime 189 The rustless iron, analyzed as follows:

Percent.

' Cr 15. 07 C O. 09 Si .0. 40

with the balance principally iron.

The chromite used in Examples III and IV contained: I

In order that the reaction may progress with the desired rapidity the ferrochromesilicon should be crushed preferably to pass about an .8-mesh screen, and the chromite should be crushed-preferably to approximately 12-mesh. The lime maybe considerably coarser, and should be wellbur'ned. I

In one form of the present process an electric furnace is employed and the mixture of ferrochrome-silicon, chromite and lime is fed under the electrical conditions which have been found most favorable to this step. The lime, the silica arising from the reaction, and the gangue of the chromite form a slag beneathwhich accumulates a bath high in chromium but quite low in carbon. 'At the convenience of the operator this slag may be retained until after the iron has been added, or replaced by a new slag forthwith. The iron is fed in liquid or solid form as may be best suited to the scale and kind of operation, and the carbon content is selected with due regard to the percentage of carbon permissible in the final product. At this stage the bath may be deoxidized by the-usual additions, the existing slag skimmed and the metal subsequently removed and handled according to.

usual steel-works practice.

If desired the steps of the process may also be undertaken in the reverse order. In this sequence the low-carbon iron may be fed in solid or liquid form and if necessary decarburized and possibly deoxidized according to usual methods. The mixture of ferrochrome-silicon, chromite and lime is then added and the bath enriched in chromium without undue increase in the carbon content. At this point the resulting slag may be replaced by one better suited to finishing the heat, which if necessary may be deoxidized before pouring.

The process may also be worked by simultaneously feeding the mixture and the iron, and finishing the resulting bath in accordance with whatever metallurgical practice the product may require.

It should be understood that the present process is not limited to the electric furnace as a means, of practicing the methodor securing the desired results. For example the described mixture may be added to a bath of iron which has been sufliciently decarburized, and if necessary deoxidized, in an open-hearth furnace and the reaction performed there, thus adding chromiumto the bath-in the desired quantity. If necessary, deoxidation of therustless iron so produced can be effected by methods and with deoxidizers well known in the metallurgy of steel.

If chromite is to be used as the source of chromium oxid, a variety presentinga relatively low ratio of iron to chromium is economlcally preferable. This will "insure a good ratio of chromium to iron in the ferrochrome-silicon, which is to say a relatively high ercentage of chromium in that alloy. The ibrrochrome-silicon should contain at least of chromium, and a considerably higher content, for example upward of is preferred. If chromite is used to oxidize the silicon of the ferrochrome-silicon, as in making a rustless iron, a chromite containing a low ratio of iron to silicon is again desirable, since evidently it will be found economical to add as much as possible of the necessary iron in the metallic form, and relatively little as iron oxid, the reduction of which by silicon is relatively-expensive.

Under some conditions the silicon contained in the high silicon alloy may be oxidized partially or wholly with oxids of .metals other than chromium, the oxid used being ofrcourse reduced in the reaction so that its metal is added to the final alloy.

Many variations of the illustrative pro cedures given above are possible and within the spirit of the invention.

I claim:

1. Process of making corrosion-resisting chromium alloys which comprises producing under electric furnace conditions a low-carbon metallic productcontaining chromium in excessof 5% and more than 40% silicon,

and then reacting on said product with a metal oxid to oxidize the silicon.

2. Process of making corrosion-resisting chromium alloys which comprises producing 4. Process of making corrosion-resisting chromium alloys which comprises producing under electric furnace conditions a metallic product containing chromium in excess of 5%, between 40 and 50% silicon, and not more than about 0.10% carbon, and then reacting on said product with a chromium oxid to oxidize the silicon.

5. An iron-chromium alloy containing upward of 40% of silicon, at least 5% of chromium, and not morethan about 0.10% of carbon.

6. An iron-chromium alloy containing between 40 and 50% of silicon, at least 5% of chromium, and not more than about 0.10% of carbon.

ture.

FREDERICK M. BECKET.

In testimony whereof, I affix mysigna- 

